Low driven inertia dual clutch

ABSTRACT

A clutch apparatus includes a clutch pack having a plurality of friction disks. The clutch pack will selectively transfer torque from a torque supplying member to a first torque receiving member. The apparatus also includes a first piston chamber positioned radially outward of the clutch pack. The first piston chamber is operably connected to the clutch pack for exerting a compressive force on at least a portion of the clutch pack as a first fluid is pressurized into the first piston chamber.

TECHNICAL FIELD

The disclosure relates to clutches for torque transmission.

BACKGROUND

Twin-clutch, twin-shaft, dual shaft, or dual clutch transmissions of thealternating shifting type are well known in the prior art. Various typesof twin clutch transmissions have been proposed and put into practicaluse, particularly in the field of wheeled motor vehicles. Traditionaltwin clutch transmissions are of a type in which gears are parted intotwo groups, each group having an individual main clutch, so that theoperative condition of each group of gears is carried out by selectivelyengaging a corresponding main clutch. Twin clutch transmissions are usedin vehicles to improve the transition from one gear ratio to anotherand, in doing so, improve the efficiency of the transmission. The gearsof each group are typically individually engaged so as to rotatablyconnect a transmission input shaft to a transmission output shaft fortransmitting torque at differing ratios. The differing ratios may beengaged by multiple shift clutches.

A typical dual clutch is illustrated in commonly owned U.S. Pat. No.7,082,850, to Hughes, the disclosure of which is hereby incorporated byreference in its entirety. Many main clutches for dual clutchtransmissions include clutch packs, having a plurality of clutch disks,for engaging and disengaging each gear group with the engine. In someapplications, the clutches are actuated by hydraulic pistons forengaging and disengaging each clutch pack. Typically, the clutch packsare located radially outside of the hydraulic pistons to prevent fluidsthat are heated by the clutch packs from contacting the outer surfacesand seals of the piston assemblies.

SUMMARY

A clutch apparatus includes a clutch pack having a plurality of frictiondisks. The clutch pack will selectively transfer torque from a torquesupplying member to a first torque receiving member. The apparatus alsoincludes a first piston chamber positioned radially outward of theclutch pack. The first piston chamber is operably connected to theclutch pack for exerting a compressive force on at least a portion ofthe clutch pack as a first fluid is pressurized into the first pistonchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, illustrative embodiments are shown indetail. Although the drawings represent some embodiments, the drawingsare not necessarily to scale and certain features may be exaggerated,removed, or partially sectioned to better illustrate and explain thepresent invention. Further, the embodiments set forth herein are notintended to be exhaustive or otherwise limit or restrict the claims tothe precise forms and configurations shown in the drawings and disclosedin the following detailed description.

FIG. 1 is a schematic illustration of a vehicle according to anembodiment.

FIG. 2 is a schematic illustration of a transmission and twin clutcharrangement according to an embodiment.

FIG. 3 is a partial sectional view of a twin clutch arrangementaccording to an embodiment.

FIG. 4 is an enlarged view of portion 4 of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 illustrates a powertrain system 20 is shown in accordance with anembodiment. In the illustrated embodiment, the powertrain system 20includes a prime mover 22, such as a spark-ignited orcompression-ignited internal combustion engine, and a transmission 24. Ashift control system 26 operates to engage and disengage gear ratioswithin the transmission 24, as discussed in greater detail below. A mainclutch assembly 28 is positioned between the prime mover 22 andtransmission 24 to selectively engage/disengage the prime mover 22 fromtransmission 24.

In an embodiment, powertrain system 20 also includes an electroniccontrol unit (ECU) 30 for controlling operation of the prime mover 22,main clutch assembly 28 generally defining an axis A-A, and transmission24. The ECU 30 may include a programmable digital computer that isconfigured to receive various input signals, including withoutlimitation, the operating speed of the prime mover 22, transmissioninput speed, selected transmission ratio, transmission output speed andvehicle speed, and processes these signals accordingly to logic rules tocontrol operation of powertrain system 20. For example, ECU 30 may beprogrammed to deliver fuel to the prime mover 22 when the prime mover 22functions as an internal combustion engine. To support this control,each of the prime mover 22, and main clutch assembly 28 may include itsown control system (not shown) contained within ECU 30. However, it willbe appreciated that the present invention is not limited to anyparticular type or configuration of ECU 30, or to any specific controllogic for governing operation of powertrain system 20. A transmissionoutput torque from an output shaft, or output member, 32 is distributedto wheels 34 through a drive shaft 36 and a differential 38.

FIG. 2, illustrates an embodiment of the transmission 24 to include afirst input shaft 40, a second input shaft 42, a countershaft 44 thatextends substantially parallel with first and second input shafts 40 and42, and a plurality of gears which are arranged on and/or around shafts40, 42 and 44. Although shafts 40, 42 and 44 are illustrated as beingmounted in a common plane in FIG. 2, these shafts may be arranged indifferent planes.

In the embodiment shown in FIG. 2, first input shaft 40 is connectableto an output member 46 of the prime mover 22, such as a flywheel,through a first main clutch C1 that is used to establish even speedgearing (viz., second speed gearing, fourth speed gearing and reversegearing), while second input shaft 42 is connectable to flywheel 46through a second main clutch C2 that is used for establishing odd speedgearing (viz., first speed gearing, third speed gearing and fifth speedgearing). In an embodiment, first and second main clutches C1 and C2 areof a normally ON type, which assumes the ON (viz., engaged) state due toa biasing force of a spring and the like under a normal condition andestablishes the OFF (viz., disengaged) state due to work of a hydraulicor electric actuator upon receiving a given instruction. Engagement anddisengagement of first and second main clutches C1, C2 may functionautomatically under the control of ECU 30, and without intervention of avehicle driver, when powertrain systems operates like an “automatic”transmission.

To first input shaft 40 there are connected a 2nd speed input gear 48, a4th speed input gear 50 and a reverse input gear 52, such that gears 48,50 and 52 rotate together with first input shaft 40. Similarly, tosecond input shaft 42 there are connected a 5th speed input gear 54, a3rd speed input gear 56 and a 1st speed input gear 58, such that gears54, 56 and 58 rotate together with second input shaft 42. The number ofinput gears provided on first and second input shafts is not limited tothe number shown in FIG. 2, and may include more or less input gearsdepending on the number of ratios desired in the transmission. The term“gear,” as stated herein, is used to define the toothed wheelsschematically illustrated in FIG. 2, as well as manufacturing thetoothed features of the wheels directly into first and second inputshafts 40, 42 and countershaft 44.

To countershaft 44 there are rotatably connected a 1st speed output gear62, a 3rd speed output gear 64, a 5th speed output gear 66, a reverseoutput gear 68, a 2nd speed output gear 70 and a 4th speed output gear72. Thus, output gears 62-72 rotate around countershaft 44. Like inputgears 48-58, the number of output gears provided on countershaft 44 isnot limited to the number schematically illustrated in FIG. 2.

Referring still to FIG. 2, 1st speed output gear 62, 3rd speed outputgear 64 and 5th speed output gear 66 are meshed with 1st speed inputgear 58, 3rd speed input gear 56 and 5th speed input gear 54,respectively. Similarly, reverse output gear 68, 2nd speed output gear70, and 4th speed output gear 72 are meshed with reverse input gear 52(through idler 94), 2nd speed input gear 48, and 4th speed input gear50, respectively. In another embodiment, transmission 24 may include asecond countershaft (not shown) that includes one or more of the outputgears rotatably disposed on first countershaft 44.

To countershaft 44 there is also integrally connected a final drivepinion gear 73 that rotates together with countershaft 44. Final drivepinion 73 is arranged perpendicular to an axis of a rotational outputmember 74, such as a final drive ring gear, and is meshed with outputmember 74. In the embodiment shown in FIGS. 1 and 2, a transmissionoutput rotation from drive pinion 73 to output member 74 is distributedto wheels 34 through a drive shaft 36 and a differential 38.

Referring again to FIG. 2, transmission 24 also includes axiallymoveable clutches 82, 84, 86 and 88, such as synchronized single ordouble acting dog-type clutches, which are splined to countershaft 44for rotation therewith. Clutch 82 is moveable by a conventional shiftfork (not shown) in an axial direction toward main clutch assembly 28 tofix countershaft 44 for rotation with 1st speed output gear 62.Similarly, clutch 84 may be moved in opposite axial directions torotationally fix output gear 64 or output gear 66 to countershaft 44.Clutch 86 may be selectively moved in opposite axial directions torotationally fix output gear 68 or output gear 70 to countershaft 44.Clutch 88 may be moved in an axial direction toward main clutch assembly28 to fix countershaft 44 for rotation with output gear 72. In anotherembodiment, clutches 82, 84, 86 and 88 may also be provided on first andsecond input shafts 40, 42 to engage and disengage gears rotatablysupported on input shafts 40, 42 in a manner substantially similar tothe manner in which the gears are engaged on countershaft 44.

In an embodiment, the transmission 24 also includes axially moveableinput shaft clutches 90 and 92, such as synchronized single actingdog-type clutches, which are splined to first input shaft 40 forrotation therewith. In the illustrated embodiment, clutch 90 may bemoved in an axial direction toward main clutch assembly 28 to fix firstinput shaft 40 for rotation with second input shaft 42. Similarly,clutch 92 may be moved in an axial direction away from main clutchassembly 28 to fix first input shaft 40 for rotation with output member74.

As described above, ECU 30 delivers commands to the components ofpowertrain system 20 based on the receipt and evaluation of variousinput signals. These commands may include gear ratio interchangecommands to a shift control device that indirectly moves clutches 82,84, 86, 88, 90 and 92 to establish the gear ratios between first andsecond input shafts 40, 42 and countershaft 44. The shift control system26 may be a conventional device, or any other suitable device thatcontrols the axial position of each of clutches 82, 84, 86, 88, 90 and92.

Operation of hybrid powertrain system 20 will now be described withreference to FIG. 2. In a first mode of operation employed duringvehicle launch and acceleration, first and second main clutches C1 andC2 are initially disengaged and clutch 82 is moved leftward from theneutral position shown in FIG. 2, so that 1st speed output gear 62 isfixed to countershaft 44 by clutch 82. Upon this movement, power fromprime mover 22 may be transmitted to countershaft 44 by engaging secondmain clutch C2. The power applied to second input shaft 42 istransmitted through 1st speed input gear 58 to countershaft 44 through1st speed output gear 62, and then to final drive pinion 73 so that afirst speed ratio is established in transmission 24.

As the vehicle accelerates and the second speed ratio is desired, clutch86 is moved rightward from the neutral position shown in FIG. 2, so that2nd speed output gear 70 is fixed to countershaft 44 by clutch 86. Theengagement of clutch 86 occurs while first main clutch C1 is disengagedand no power is being transmitted from prime mover 22 to first inputshaft 40. Once clutch 86 is engaged, the currently engaged second mainclutch C2 is disengaged while simultaneously or nearly simultaneouslyengaging first main clutch C1. The resulting power applied to firstinput shaft 40 is transmitted through 2nd speed input gear 48 tocountershaft 44 through 2nd speed output gear 70, and then to finaldrive pinion 73 so that a second speed ratio is established intransmission 24. This process is repeated, including the selectiveactivation of the appropriate clutch, in the same manner for up-shiftingthrough the remaining gear ratios, and in a reverse manner fordown-shifting from one gear ratio to another.

To achieve the reverse gear in transmission 24, first and second mainclutches C1 and C2 are disengaged and clutch 86 is moved leftward fromthe neutral position shown in FIG. 2, so that reverse output gear 68 isfixed to countershaft 44 by clutch 86. The power applied to first inputshaft 40 is transmitted from reverse input gear 52 to countershaft 44through an idler gear 94 and reverse output gear 68, and then to finaldrive pinion 73.

Under a normal operating state, wherein transmission 24 assumes acertain speed gearing, both first and second main clutches C1 and C2 maybe kept in their engaged conditions while one of clutches 82, 84, 86,and 88 is kept at a given power transmitting position. For example, whentransmission 24 assumes the 5th speed ratio, both first and second mainclutches C1 and C2 may be engaged while clutch 84 is engaged with 5thspeed output gear 66 and clutches 82, 86 and 88 are in their neutralposition shown in FIG. 2. Although first and second main clutches areengaged, no power is transmitted through the unselected output gears 62,64, 68, 70 and 72 because the output gears are free to rotate oncountershaft 44 when not engaged by a corresponding clutch 82, 86 or 88.

In the embodiment shown in FIG. 2, gears 58 and 62 establish a “low”gear ratio between second input shaft 42 and countershaft 44 when clutch82 fixes gear 62 for rotation with countershaft 44. Gears 54 and 66establish a “high” gear ratio between second input shaft 42 andcountershaft 44 when clutch 84 fixes gear 66 for rotation withcountershaft 44.

As best seen in FIG. 3, the main clutch assembly 28 includes a housing100, a damper 102, a clutch collar 104, a clutch drum 106, a firstclutch hub 108, a second clutch hub 110, a first piston assembly 114,and a second piston assembly 116.

The housing 100 is connected to a portion of the transmission 24 and theprime mover 22. In the embodiment illustrated, the damper 102 is alubricated noise, vibration and harshness (NVH) damper for reducing atleast undesired drivetrain torque oscillations and other vibrations. Theclutch drum 106 is coupled to an outer portion of the damper 102 forrotation therewith.

In the embodiment illustrated, the clutch drum 106 includes a pluralityof annular first drum disks 122 and a plurality of annular second drumdisks 124 extending radially therefrom. The first clutch hub 108includes a plurality of annular first hub disks 128 extending radiallytherefrom. The second clutch hub 110 includes a plurality of annularsecond hub disks 130 extending radially therefrom. The first drum disks122 are interleaved with the first hub disks 128, and the second drumdisks 124 are interleaved with the second hub disks 130, as described ingreater detail below.

FIG. 4 illustrates an enlarged portion of the main clutch assembly 28 ofFIG. 3. As best seen in FIG. 4, the first drum disks 122 include a firstpressure plate 140, a first drum first disk 142, a first drum seconddisk 144, a first drum third disk 146, and a first reaction plate 148.The second drum disks 124 include a second pressure plate 150, a seconddrum first disk 152, a second drum second disk 154, a second drum thirddisk 156, and a second reaction plate 158. The first hub disks 128include a first hub first disk 162, a first hub second disk 164, a firsthub third disk 166, and a first hub fourth disk 168. The second hubdisks 130 include a second hub first disk 172, a second hub second disk174, a second hub third disk 176, and a second hub fourth disk 178.

The first pressure plate 140 includes a first pressure plate forwardsurface 180 and a first pressure plate rearward surface 182. The firstdrum first disk 142 includes a first drum first disk forward surface 184and a first drum first disk rearward surface 186. The first drum seconddisk 144 includes a first drum second disk forward surface 188 and afirst drum second disk rearward surface 190. The first drum third disk146 includes a first drum third disk forward surface 192 and a firstdrum third disk rearward surface 194. The first reaction plate 148includes a first reaction plate forward surface 196 and a first reactionplate rearward surface 198.

The second pressure plate 150 includes a second pressure plate forwardsurface 200 and a second pressure plate rearward surface 202. The seconddrum first disk 152 includes a second drum first disk forward surface204 and a second drum first disk rearward surface 206. The second drumsecond disk 154 includes a second drum second disk forward surface 208and a second drum second disk rearward surface 210. The second drumthird disk 156 includes a second drum third disk forward surface 212 anda second drum third disk rearward surface 214. The second reaction plate158 includes a second reaction plate forward surface 216 and a secondreaction plate rearward surface 218.

The first hub first disk 162 includes a first hub first disk forwardsurface 220 and a first hub first disk rearward surface 222. The firsthub second disk 164 includes a first hub second disk forward surface 224and a first hub second disk rearward surface 226. The first hub thirddisk 166 includes a first hub third disk forward surface 228 and a firsthub third disk rearward surface 230. The first hub fourth disk 168includes a first hub fourth disk forward surface 232 and a first hubfourth disk rearward surface 234.

The second hub first disk 172 includes a second hub first disk forwardsurface 240 and a second hub first disk rearward surface 242. The secondhub second disk 174 includes a second hub second disk forward surface244 and a second hub second disk rearward surface 246. The second hubthird disk 176 includes a second hub third disk forward surface 248 anda second hub third disk rearward surface 250. The second hub fourth disk178 includes a second hub fourth disk forward surface 252 and a secondhub fourth disk rearward surface 254.

The first piston assembly 114 includes an annular first apply plate 260,an annular first piston 262, an annular first return spring 264. Thefirst piston 262 includes a first piston reaction surface 266 and afirst piston apply surface 268. The second piston assembly 116 includesan annular second apply plate 270, an annular second piston 272, anannular second return spring 274. The second piston 272 includes asecond piston reaction surface 276 and a second piston apply surface278. The clutch drum 106, the first apply plate 260 and the first piston262 define an annular first piston chamber 280. The clutch drum 106, thesecond apply plate 270 and the second piston 272 define an annularsecond piston chamber 282. The first piston assembly 114 and the secondpiston assembly 116 include annular piston seals 290 for sealing thepiston chambers 280, 282. In the embodiment illustrated, the firstreturn spring 264 is axially restrained by a first piston retaining ring292 and a first drum retaining ring 294. The second return spring 274 isaxially restrained by a second piston retaining ring 296 and a seconddrum retaining ring 298.

In the embodiment illustrated, the piston seals 290 are constructed of amaterial that will withstand heated fluid from the clutch disks 122,124, 128, 130, such as DuPont™ Vamac®, or other suitable material.

The clutch collar 104 supplies fluid to the clutch drum 106, whichsupplies fluid to the first piston assembly 114, the second pistonassembly 116, and the clutch disks as discussed in greater detail below.The clutch drum 106 includes a first piston chamber port 300, and asecond piston chamber port 302. The shafts 40, 42 define a first clutchcooling port 304 and a second clutch cooling port 306. The clutch collar104 is adapted to supply a cooling fluid (not shown) to the ports 300,302 and control the pressure thereof, as is conventionally known.

The clutch drum 106 is further defined by a central web 310, an annularfirst balance chamber wall 312, a cylindrical first balance chamberconnecting wall 314, a second balance chamber wall 316, and acylindrical second balance chamber connecting wall 318. The first piston262, the first balance chamber wall 312, and the first balance chamberconnecting wall 314 define a first balance chamber 320. The clutch drum106 is also defined by a first coolant passage 322, a first reservoir324, a first cooling first inlet 326, a first cooling second inlet 328,a first cooling third inlet 330, and a first cooling fourth inlet 332.The second piston 272, the second balance chamber wall 316, and thesecond balance chamber connecting wall 318 define a second balancechamber 340.

As the main clutch assembly 28 rotates about the axis A-A (FIG. 3),fluid supplied through the ports 300, 302, 304, 306 will tend to rotatewith the main clutch assembly 28 and will be accelerated away from theaxis A-A. As fluid present within the first piston chamber 280 and thesecond piston chamber 282 is accelerated away from the axis A-A, thefluid will bias the respective piston 262, 272 away from the respectiveapply plate 260, 270 and act against the biasing force of springs 264,274. Additionally, the fluid supplied through the ports 304, 306 willcool the clutch disks 122, 124 then fill the balance chambers 320, 340.

When fluid pressure is supplied through the first piston chamber port300, the first piston 262 will move in the rearward direction(illustrated as the arrow R in FIGS. 3 and 4) as the first apply plate260 remains generally stationary relative to the clutch hub 106. Thefirst return spring 264 is axially deflected due to interference betweenthe first piston retaining ring 292 and the first hub retaining ring 294as the first piston 262 moves in the direction R, biasing the firstpiston in the direction of arrow F. As the first piston 262 moves in thedirection R, the first piston will move toward the first balance chamberwall 312 and reduce the volume of fluid within the first balance chamber320. Generally, the volume of fluid that is forced into the first pistonchamber 280 is equal to the volume of fluid that is displaced from thefirst balance chamber 320, thereby maintaining the rotational weight andthe rotational inertia of the main clutch assembly 28.

As the first piston 262 moves in the direction of the arrow, the firstpiston reaction surface 266 urges the first pressure plate 140 towardthe first reaction plate 148, thereby actuating the first clutch C1.While the first clutch C1 and the second clutch C2 are illustrated as aclutch pack having interleaved disks, the clutches used in the mainclutch assembly may be any clutch configuration, having any number ofengaging frictional surfaces.

By providing components of the main clutch assembly 28, such as theclutch disks 122, 124, 128, 130 interposed radially within the pistonassemblies 114, 116, the resulting clutch assembly may have a desirablyshorter axial length when compared to clutch assemblies that havecomponents orientated solely in an axial orientation. Generally, theweight of the clutch disks 122, 124, 128, 130 is greater than the weightof the piston assemblies 114, 116. Accordingly, positioning the clutchdisks 122, 124 radially inward of the piston assemblies 114, 116 willresult in a main clutch assembly 28 with a lower rotational inertia whencompared to a clutch assembly having clutch packs positioned radiallyoutward of piston assemblies. In the embodiment illustrated, the clutchdisks 122, 124, 128, 130 are axially adjacent with a minimum number ofclutch components positioned between the clutch disks 122, 124, 128, 130and the shafts 40, 42 to further decrease the rotational inertia of themain clutch assembly 28.

The preceding description has been presented only to illustrate anddescribe exemplary embodiments of the methods and systems of the presentinvention. It is not intended to be exhaustive or to limit the inventionto any precise form disclosed. It will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from the essential scope. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe claims. The invention may be practiced otherwise than isspecifically explained and illustrated without departing from its spiritor scope. The scope of the invention is limited solely by the followingclaims.

1-20. (canceled)
 21. A clutch apparatus comprising: a clutch pack havinga plurality of friction disks that selectively transfer torque from atorque supplying member to a torque receiving member; a piston chamberpositioned radially outward of the clutch pack and operably connected tothe clutch pack for exerting a compressive force on a piston as a fluidis forced into the piston chamber from a piston chamber port; and abalance chamber formed at least partially between the piston and a wallof the balance chamber; wherein: as the fluid is forced into the pistonchamber port, the fluid is displaced from the balance chamber; and avolume of the fluid that is forced into the piston chamber is generallyequal to a volume of the fluid that is displaced from the balancechamber, thereby maintaining a rotational weight and a rotationalinertia of the clutch apparatus.
 22. The apparatus of claim 21, furthercomprising a return spring axially restrained by a piston retaining ringand a drum retaining ring, wherein the return spring provides an axialbiasing force in a first direction upon the piston.
 23. The apparatus ofclaim 22, wherein when the fluid is forced into the piston chamber, thepiston is caused to displace axially in a second direction that isopposite the first direction.
 24. The apparatus of claim 21, wherein theclutch pack includes a clutch hub coupled to a plurality of hub disksand a clutch drum coupled to a plurality of drum disks, wherein at leasta subset of the hub disks are interleaved with the drum disks.
 25. Theapparatus of claim 24, wherein the clutch hub is splined for mating witha transmission input shaft.
 26. The apparatus of claim 21, wherein thepiston chamber port is positioned radially external to the pistonchamber, and wherein the piston chamber port is in fluid connection withthe piston chamber to provide the fluid to the piston chamber.
 27. Theapparatus of claim 21, further comprising an annular piston sealpositioned between the piston chamber and the balance chamber forsealing the piston chamber from the balance chamber.
 28. A torquetransmitting apparatus for a vehicle, comprising: a first clutch packhaving a plurality of friction disks that selectively transfer torquefrom a torque supplying member to a first torque receiving member; asecond clutch pack having a plurality of friction disks that selectivelytransfer torque from the torque supplying member to a second torquereceiving member; wherein each of the first and second clutch packsinclude: a piston chamber positioned radially outward of the clutch packand operably connected to a respective clutch pack for exerting acompressive force on a piston as a fluid is pressurized into eachrespective piston chamber from a respective piston chamber port; and abalance chamber formed at least partially between each piston and a wallof a respective balance chamber, wherein a volume of the fluid that isforced into the respective piston chamber is generally equal to a volumeof the fluid that is displaced from the respective balance chamber,thereby maintaining a rotational weight and a rotational inertia of eachclutch pack.
 29. The torque transmitting device of claim 28, whereineach of the first and second clutch packs include a return springaxially restrained by a piston retaining ring and a drum retaining ring,wherein each return spring provides an axial biasing force upon eachrespective piston such that the pistons are biased away from one anotherby their respective return spring.
 30. The torque transmitting device ofclaim 29, wherein when the fluid is displaced into each respectivepiston chamber, the pistons are caused to displace axially toward oneanother.
 31. The torque transmitting device of claim 28, wherein eachclutch pack includes a clutch hub coupled to a plurality of hub disksand a clutch drum coupled to a plurality of drum disks, wherein at leasta subset of the hub disks are interleaved with the drum disks.
 32. Thetorque transmitting device of claim 31, wherein each clutch hub issplined for mating with a transmission input shaft.
 33. The torquetransmitting device of claim 28, wherein each respective port ispositioned radially external to its piston chamber, and wherein the portis in fluid connection with the respective piston chamber to provide thefluid into the respective piston chamber.
 34. The torque transmittingdevice of claim 28, wherein each clutch pack includes an annular pistonseal positioned between each respective piston chamber and balancechamber for sealing them from one another.
 35. A torque transmittingapparatus for a vehicle, comprising: a first clutch that selectivelytransfers torque from a torque supplying member to a first torquereceiving member; a second clutch that selectively transfers torque fromthe torque supplying member to a second torque receiving member; a firstpiston assembly positioned radially outward of the first clutch andincluding a first piston for exerting an axial force on the first clutchvia a first amount of a fluid; and a second piston assembly positionedradially outward of the second clutch and including a second piston forexerting an axial force on the second clutch via a fluid; wherein eachof the first and second clutch packs include a balance chamber formed atleast partially between the respective piston and a wall of therespective balance chamber, wherein a volume of the fluid that is forcedinto the respective piston chamber is equal to a volume of the fluidthat is displaced from the respective balance chamber, therebymaintaining a rotational weight and a rotational inertia of each clutchpack.
 36. The apparatus of claim 35, wherein each of the first andsecond clutch packs includes a return spring axially restrained by apiston retaining ring and a drum retaining ring, wherein each returnspring provides an axial biasing force upon each respective piston suchthat the pistons are biased away from one another by their respectivereturn spring.
 37. The torque transmitting device of claim 36, whereinwhen the fluid is displaced into each respective piston chamber, thepistons are caused to displace axially toward one another.
 38. Thetorque transmitting device of claim 35, wherein each clutch packincludes a clutch hub coupled to a plurality of hub disks and a clutchdrum coupled to a plurality of drum disks, wherein at least a subset ofthe hub disks are interleaved with the drum disks.
 39. The torquetransmitting device of claim 38, wherein each clutch hub is splined formating with a transmission input shaft.
 40. The torque transmittingdevice of claim 35, wherein each clutch pack includes a respective portpositioned radially external to its piston chamber, wherein the port isin fluid connection with the respective piston chamber to provide thefirst fluid into the piston chamber.